The present invention relates to an oil pump for feeding lubricating oil to various slide portions of an internal combustion engine, for example.
A trochoid oil pump for an automotive internal combustion engine comprises a pump casing formed with inlet and outlet ports formed in both sides, and a drive shaft arranged through the pump casing roughly in the center for receiving torque of an engine crankshaft. Arranged rotatably in the pump casing are an inner rotor coupled to the drive shaft and including external teeth at the outer periphery, and an outer rotor including internal teeth meshed with the external teeth of the inner rotor.
With rotation of the inner and outer rotors, volume chambers defined between the internal and external teeth of the rotors vary in volume to discharge to the outlet port lubricating oil inhaled through the inlet port, ensuring pump action. Excess oil discharged through the outlet port is returned from a relief valve to the low-pressure side (inlet-port side), achieving the discharge pressure controlled at a given value.
With the oil pump, however, since lubricating oil inhaled through the inlet port is discharged to the outlet port while being compressed due to volume variation in the volume chambers as described above, pulsation at a certain period occurs to cause sideward oscillation of the relief valve, opening/closing a relief port. This can amplify pulsation to produce relatively great noise at the discharge side.
With the aim of reducing pulsation, Japanese document P2003-184523A teaches an oil pump which comprises a bent wall arranged downstream of the outlet port and a branch passage arranged downstream of the bent wall to reverse the direction of oil flow, whereby oil out of the outlet port is made to flow from the bent wall to the branch passage.